USB / RS485 communication

Hello
I design my application that i have tested under RS232 communications and it work's good with a USB/RS232 converter.
Now I need to change to RS485 instaed the RS232 to send and to receive data from my programm in the PC.
For that, I draw a pcb with the circuit schematic suggested in the FT232RL datasheet.
Unhappily doesn't work correctly, it freezes the communication, so that I have to remove the Usb connector in the PC and connect it again to open again a virtual COM. I think have to read, that is possible to do a Usb/RS485 convertor with a PIC microcontroller that automatically switch between receiving and transmition on the Max487. If somebody can help or already came across this problem and solved it other way I am thankful for some tips

Regards
Pedro